1. Field of the Invention
The present invention relates to an optical device having a light incident surface, a light emitting surface and a light-reflecting side surface, all of which are mirror-finished, and a projection-type image display apparatus including the optical device.
2. Description of the Related Art
A projection-type image display apparatus including a light source, an optical modulation element (for example, a liquid crystal panel), a projection lens and the like has been generally well-known. Moreover, as such a projection-type image display apparatus, a projection-type image display apparatus has also been known which includes an optical device (hereinafter referred to as a rod integrator) for the purpose of uniformizing intensity of light emitted by the light source, and the like.
As such a rod integrator, cited is a rod integrator formed of a hollow rod, and provided with a mirror which is formed on an inner surface of the hollow rod, and which reflects light emitted by a light source (for example, Japanese Patent Publication No. 2005-316405 (Claim 6, [0023], FIG. 3)).
Moreover, another known rod integrator is formed of a glass solid rod, and a surface of the solid rod is mirror-finished. By use of this rod integrator, light emitted by a light source is totally reflected on a side surface of the solid rod. Thus, intensity of the light emitted by the light source can be uniformized while suppressing reduction in efficiency in use of the light emitted by the light source.
Meanwhile, in order to reduce costs for the projection-type image display apparatus, demanded is an optical device (a rod integrator) at low cost than the rod integrator having the mirror provided on the inner surface of the hollow rod, or than the rod integrator formed of the glass solid rod.
Consequently, the inventors have focused attention on an optical device which is formed of a solid rod of transparent resin, and in which a surface of the solid rod is mirror-finished.
However, since the above optical device is formed of the solid rod made of transparent resin, a surface thereof is easily scratched in the processes of manufacturing the projection-type image display apparatus, and the like. Furthermore, when the surface of the optical device is scratched, total reflection of the light emitted by the light source is no longer achieved. Consequently, the efficiency in use of the light emitted by the light source is reduced.